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Dandruff is a condition that creates white, itchy flakes on the scalp. These flakes may fall into hair and on shoulders, making an embarrassing and unsightly mess. According to the Mayo Clinic, dandruff can be caused by psoriasis; eczema; not shampooing hair enough; dry skin; seborrheic dermatitis, a condition that creates itchy and oily skin; or malassezia, a fungus. Washing the hair and scalp with a gentle shampoo may help eliminate mild cases of dandruff, says the Mayo Clinic, but if dandruff is more severe, medicated shampoos that prevent skin cells from flaking or that help remove dead skin cells and fungus might be necessary.

Coal Tar Shampoo

Shampoos that contain coal tar are available over the counter and are effective in treating dandruff caused by seborrheic dermatitis and psoriasis, says the Mayo Clinic. Coal tar extends the life of the skin cells on the scalp, preventing them from flaking off as quickly as those on an untreated scalp.

Zinc Pyrithione Shampoo

Zinc pyrithione, an active ingredient in a variety of over-the-counter dandruff shampoos, is an anti-fungal agent. It is one of the most effective agents at keeping dandruff at bay, according to Health Services at Columbia. Zinc pyrithione works to reduce fungus that causes seborrheic dermatitis and malassezia.

Ketoconazole Shampoo

Ketoconazole treats dandruff that is caused by fungus. It is also a common treatment for a variety of other fungal infections and is used when dandruff does not respond to other dandruff shampoos. Ketoconazole is available both over the counter and as a prescription.

Selenium Sulfide Shampoo

Shampoos that contain selenium sulfide keep skin cells from shedding and may be effective in treating malassezia. Selenium sulfide shampoos may discolor light hair and is not recommended for individuals with blond, gray or dyed hair.

Salicylic Acid Shampoo

Salicylic acid shampoo may help remove dead skin cells that have built up on the scalp and cause dandruff. Salicylic acid shampoo may cause dry skin, however, which can also create dandruff. Condition your hair after using salicylic acid shampoo to reduce dry skin.